This research proposal is concerned with a detailed study of the mechanism of reduction of ribonucleotides by ribonucleotide reductase and the design of potential suicide inhibitors for this enzyme. Specifically, a new mechanism for this reduction is proposed, involving generation of a radical cation intermediate. This mechanism is consistent with the experimental facts and is based on several recent chemical model systems. This mechanism can be tested using specifically labeled substrates. While the mechanistic studies will be performed on the E. coli system, additional experiments have been described to further clarify the similarities and differences of the E. coli and mammalian enzymes. In particular, interaction of mammalian RNR with 2' chloro, fluoro and azido-deoxynucleotides will be investigated. Finally, using mechanistic information obtaind from these studies and previous studies, we will synthesize a number of potential suicide inhibitors for ribonucleotide reductase, which are nucleotide analogs which contain radical scavengers at the 2' position. Reaction of these analogs, after chemical modification by the enzyme should generate a radical scavenger at the active site, which may quench the enzyme radical, resulting in specific inactivation. Promising inhibitors will be further tested in a number of tissue culture systems. The mechanistic information obtained about ribonucleotide reductase and the design of specific inhibitors based on this information could have important implications in cancer chemotherapy.